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Temperature Chambers and Environmental Test Chambers
The best way to understand how a product or material will perform in the field or over time is to use a laboratory test chamber to model those conditions. This is done in one of two ways: the test chamber may model the conditions exactly as they are, or the chamber may accelerate aging of the material, subjecting it to years worth of stress in hours or days. Many of these tests are associated with high-stakes applications, where millions of dollars of equipment, or even lives, are on the line. Some test chamber applications must comply with rigorous governmental regulations, such as FDA guideline 21 CFR part 11. This means, that the materials, components, and technologies used in constructing these chambers must be tougher than anything put inside of them, and that the chamber must meet very high performance standards.
Some of the most extreme laboratory test chambers are used by NASA to test equipment for space flight and exploration. Components intended for the Hubble space telescope or the International Space Station undergo simulated space conditions in NASA's large test chambers at the NASA Goddard Space Center in Maryland. This testing includes a centrifuge, a thermal vacuum chamber for extreme hot or cold conditions, and an acoustic chamber capable of noise up to 150 db.
Compared to these NASA super chambers, most laboratory and industrial test chamber needs are modest. There is no one test chamber that can meet every need, but a wide variety of single-variable and combination environmental test chambers are available to simulate almost any set of conditions you could imagine. Chambers can be as large as a garage, but more often are proportioned to fit in the corner of a laboratory or on a bench top. Many types of test chambers are available, depending on the application and needs. Temperature chambers offer adjustable temperatures only. Other chambers, usually called stability or humidity chambers, offer a range of humidity conditions. Climate chambers simulate conditions of temperature and humidity, and environmental chambers include additional variables, such as light, motion, or dust.
A temperature chamber is the most basic of laboratory test chambers. A variety of technologies and hardware are available in a temperature test chamber. The temperature may be modulated by electric coils, gravity convection, fan-driven convection, or a circulating water bath. One distinguishing feature of a temperature chamber is the broad temperature range available: some models go as low as -80°C, while the maximum temperatures can be 300°C or higher. Precision and accuracy in temperature settings is important. The actual temperature inside the oven should match as closely as possible the desired temperature, and most ovens are precise to within a few tenths of a degree. As well, evenness of temperature is a major issue in a temperature chamber; there should be no hot or cold spots within the chamber. For this reason, most temperature test chambers include a system for circulating air.
Another important feature in a temperature test chamber is the temperature change rate. It is sometimes desirable to test an item at a number of different temperatures. The amount of time spent moving from one temperature to another represents some degree of uncertainty in the experimental results. Rapid temperature change rates can minimize this uncertainty. Alternatively, temperature chambers with programmable change rates give users the ability to design gradient experiments.
Humidity chambers (also called stability chambers) are most in-demand in industries that package, store, and transport products that are sensitive to moisture, such as the pharmaceutical industry or food packaging. A humidity test chamber will offer a temperature control, but the range reflects what would be found in a normal indoor or outdoor environment—from around 0°C to 100°C. Relative humidity within the chamber can be as low as 10% or as high as 98%. All of the components of the stability chamber must be made of a corrosion resistant material such as stainless steel. A humidity sensor on the inside is an added feature that can improve the accuracy of the device.
Temperature Humidity Chambers
Temperature humidity chambers (also known as climate test chambers) combine temperature and humidity controls for more rigorous testing conditions. With an extended temperature range similar to a temperature chamber (above) in addition to a humidity control system, the temperature humidity chamber is a specialized piece of equipment for advanced applications. Climate chambers are used extensively in testing semiconductors, where a small amount of corrosion can cause a major failure of an electronic device. This is especially true with electronics that are exposed to outdoor weather conditions, such as military equipment, telecommunications equipment, or photovoltaic solar panels.
Environmental Test Chambers
In addition to temperature and humidity, many other aspects of an environment can be modeled and simulated using an environmental test chamber. Environmental chambers that include a pressure control can model low or high altitude conditions, or deep-sea environments. Some test chambers incorporate environmental elements such as light, dust, rain, or motion. An environmental chamber may vibrate, rotate, or shock its contents to mimic rough handling in the field. Light and wind are other stressors that can be incorporated into the chamber.
Laboratory test chambers have applications across a wide range of science and engineering disciplines. Industrial uses for test chambers include product stability testing, accelerated aging, shelf life, and test-to-failure. Research uses for test chambers include everything from incubations of delicate biological experiments to simulating extreme conditions on Earth or even in outer space. The choice of a laboratory test chamber is an important decision, because it will be one of the most used (and abused) pieces of equipment in the lab.